1. Field of Invention
The present invention relates to a static pressure air bearing having two axes, a lower axis and an upper axis, used in a vacuum environment.
2. Description of Related Art
Conventional static pressure air bearings having two axes used in a vacuum environment have been provided with air exhaust pipes connected with the movable part of each axis bearing mechanism. That is, each axis has its own dedicated air exhaust pipes, which are connected to the movable part of each axis. Therefore, air exhaust from each axis bearing has been separately done.
The conventional air exhaust method requires, with respect to the upper axis, the connection of the air exhaust pipe with the movable part of the upper axis bearing mechanism. Additionally, a large bore diameter of the pipe is required to obtain efficient air exhaust displacement. These features cause a great resistance to the feeding motion of the bearing and seriously affect the bearing performance. This problem arises when the air exhaust pipe is connected with the movable part of the upper axis, and also arises when the air exhaust pipe is connected with inner piping formed within a fixed part of the upper axis (because the fixed part of the upper axis also moves).
The present invention provides a static pressure air bearing having two axes usable in a vacuum environment in which the connection of the supporting air exhaust pipe does not adversely affect the motion of the bearing mechanism.
To accomplish the above and/or others objects, according to one aspect of the present invention, there is provided a static pressure air bearing having two axes, a lower axis and an upper axis, in which inner air exhaust piping formed within a fixed part of the lower axis and inner air exhaust piping formed within a fixed part of the upper axis (which is fixed on a movable part of the lower axis) communicate with each other.
Through the implementation of the above configuration, the air exhaust pipe can be connected only with the fixed part of the lower axis and need not be directly connected with the movable parts of the bearing mechanism. Consequently, an air exhaust pipe of a large bore diameter does not adversely affect the bearing performance.
In a preferred embodiment of the present invention, the communication between the inner air exhaust piping of the fixed part of the lower axis and the inner air exhaust piping of the fixed part of the upper axis is provided through air exhaust communication grooves and air exhaust communication piping formed within the movable part of the lower axis. Through the implementation of the above configuration, the air exhaust pipe need not be connected directly with the fixed part of the upper axis. Thus, because there is no connection of the air exhaust pipe with any of the moving parts of the bearing mechanism, the air exhaust pipe does not adversely affect the bearing performance, e.g., rectilinear feeding accuracy.
In a preferred embodiment of the present invention, the supporting air is exhausted through the inner air exhaust piping formed within the fixed parts of the lower and upper axes. Through the above configuration, the air exhaust pipe need not be connected either with the movable part of the lower axis or with the movable part of the upper axis.
In a preferred embodiment of the present invention, air exhaust grooves are disposed surrounding each air pad of the lower and upper axes. Through the above configuration, because only a limited amount of air can flow into the vacuum chamber from the gap of the bearing, the bearing is usable in a vacuum environment.
In a preferred embodiment of the present invention, air supply structure is also accommodated in the fixed parts. That is, inner air supply piping formed within the fixed part of the lower axis and inner air supply piping formed within the fixed part of the upper axis (which is attached to the movable part of the lower axis) communicate with each other. Through the above configuration, because both the air supply and the air exhaust are done within the fixed parts, tubing connection with the movable parts can also be avoided.